1. Field of the Invention
The present invention relates to an emissive display device and, more particularly, to an organic light emitting device (OLED) display and a method of time-divisionally driving two light emitting elements among R, G and B electroluminescent (EL) elements of two adjacent pixels.
2. Description of the Related Art
Recently, liquid crystal displays (LCDs) and OLED displays are widely used as portable information displays having features such as light weight, thin profile, and the like. The OLED displays have better performance in terms of luminance and wide viewing angle than LCDs, such that they attract an attention as next generation flat panel displays.
Generally, in an active matrix OLED display, one pixel is composed of R, G and B unit pixels each including an EL element. In each EL element, an R, G or B organic emission layer is interposed between an anode electrode and a cathode electrode, so that light is emitted from the R, G and B organic emission layers by voltages applied to the anode electrode and the cathode electrode.
FIG. 1 illustrates a configuration of a conventional active matrix OLED 10.
Referring to FIG. 1, the conventional active matrix OLED 10 includes a pixel portion 100, a gate line driving circuit 110, a data line driving circuit 120 and a control unit (not shown). The pixel portion 100 includes a plurality of gate lines 111-11m to which scan signals S1-Sm are provided from the gate line driving circuit 110, a plurality of data lines 121 (121R, 121G, 121B)-12n (12nR, 12nG, 12nB) for supplying data signals (DR1, DG1, DB1)-(DRn, DGn, DBn) from the data line driving circuit 120, and a plurality of power lines 131 (131R, 131G, 131B) to 13n (13nR, 13nG, 13nB) for providing power supply voltages VDD1-VDDn.
In the pixel portion 100, a plurality of pixels P11-Pmn connected to the plurality of gate lines 111-11m, the plurality of data lines 121-12n, and the plurality of power lines 131-13n are arranged in a matrix form. Each of the pixels P11-Pmn is composed of three unit pixels, i.e., R, G and B unit pixels (PR11, PG11, PB11)-(PRmn, PGmn, PBmn), and is connected to the corresponding one gate line, one data line and one power supply line of the plurality of gate lines, data lines, and power supply lines.
For example, the pixel P11 is composed of an R unit pixel PR11, a G unit pixel PG11 and a B unit pixel PB11. The pixel P11 is connected to a first gate line 111 of the plurality of gate lines 111-11m that provides a first scan signal S1, a first data line of the plurality of data lines 121-12n, and a first power line 131 of the plurality of power lines 131-13n. 
In other words, the R unit pixel PR11 of the pixel P11 is connected to the first gate line 111, an R data line 121R, to which an R data signal DR1 is provided, of the first data lines 121, and an R power line 131R of the first power lines 131. The G unit pixel PG11 is connected to the first gate line 111, a G data line 121G, to which a G data signal DG1 is provided, of the first data lines 121, and a G power line 131G of the first power lines 131. The B unit pixel PB11 is connected to the first gate line 111, a B data line 121B, to which a B data signal DB1 is provided, of the first data lines 121, and a B power line 131B of the first power lines 131.
FIG. 2 shows a pixel circuit of the conventional OLED, illustrating a circuit diagram of one pixel P11 composed of R, G and B unit pixels.
Referring to FIG. 2, the R unit pixel PR11 of the R, G and B unit pixels PR11, PG11, PB11 constituting the pixel P11 includes a switching transistor M1_R in which the scan signal S1 applied from the first gate line 111 is provided to a gate, and the data signal DR1 from the R data line 121R is provided to a source. The R unit pixel PR11 also includes a driving transistor M2_R in which a gate is connected to a drain of the switching transistor M1_R and the power supply voltage VDD1 from the power supply line 131R is provided to a source. A capacitor C1_R is connected between the gate and the source of the driving transistor M2_R. In addition, the R unit pixel PR11 includes an R EL element EL1_R in which an anode is connected to a drain of the driving transistor M2_R and a cathode is connected to a ground voltage VSS.
Likewise, the G unit pixel PG11 includes: a switching transistor M1_G in which the scan signal S1 applied from the first gate line 111 is provided to a gate, and the data signal DG1 from the G data line 121G is provided to a source. The G unit pixel PG11 also includes a driving transistor M2_G in which a gate is connected to a drain of the switching transistor M1_G and the power supply voltage VDD1 from the power supply line 131G is provided to a source. A capacitor C1_G is connected between the gate and the source of the driving transistor M2_G. In addition, the G unit pixel PG11 includes a G EL element EL1_G in which an anode is connected to a drain of the driving transistor M2_G and a cathode is connected to the ground Vss.
Further, the B unit pixel PB11 includes a switching transistor M1_B in which the scan signal S1 applied from the first gate line 111 is provided to a gate and the data signal DB1 from the B data line 121B is provided to a source. The B unit pixel PB11 also includes a driving transistor M2_B in which a gate is connected to a drain of the switching transistor M1_B and the power supply voltage VDD1 from the power supply line 131B is provided to a source. A capacitor C1_B is connected between the gate and the source of the driving transistor M2_B. In addition, the B unit pixel PB11 includes a B EL element EL1_B in which an anode is connected to the drain of the driving transistor M2_B and a cathode is connected to the ground voltage VSS.
In an operation of the pixel circuit illustrated above, when the scan signal S1 is applied to the gate line 111, the switching transistors M1_R, M1_G, M1_B of the R, G and B unit pixels constituting the pixel P11 are driven thereby, and the R, G and B data DR1, DG1, DB1 from the R, G and B data lines 121R, 121G, 121B are applied, respectively, to the gates of the driving transistors M2_R, M2_G, and M2_B.
The driving transistors M2_R, M2_G, M2_G provide the EL elements EL1_R, EL1_G, EL1_B with respective driving currents corresponding to a difference between the data signals DR1, DG1, DB1 applied to the gates and the power supply voltage VDD1 supplied from respective R, G and B power supply lines 131R, 131G, 131B. The EL elements EL1_R, EL1_G, EL1_B are driven by the driving currents applied through the respective driving transistors M2_R, M2_G, M2_B, thereby resulting in driving the pixel P11. The capacitors C1_R, C1_G, C1_B store the respective data signals DR1, DG1, DB1 applied to the R, G and B data lines 121R, 121G and 121B.
The operation of the conventional OLED having a configuration as illustrated above will now be described with reference to the driving waveform diagram of FIG. 3.
First, when the scan signal S1 is applied to the first gate line 111, the first gate line is driven, and then, the pixels P11-P1n connected to the first gate line 111 are driven.
In other words, the switching transistors of the R, G and B unit pixels (PR11-PR1n), (PG11-PG1n), (PB11-PB1n) of the pixels P11-P1n connected to the first gate line 111 are driven by the scan signal S1 applied to the first gate line 111. When the switching transistors are driven, the R, G and B data signals D(S1) (DR1-DRn), (DG1-DGn), (DB1-DBn) from the R, G and B data lines (121R-12nR), (121G-12nG), (121B-12nB) constituting the first to the nth data lines 121 to 12n are respectively applied to the gates of the driving transistors of the R, G and B unit pixels at the same time.
The driving transistors of the R, G and B unit pixels provide the R, G and B EL elements with the driving currents corresponding to the R, G and B data signals D (S1) (DR1 to DRn), (DG1 to DGn), (DB1 to DBn) each applied to the R, G and B data lines 121R to 121nR, 121G to 12nG, 121B to 12nB. Therefore, when the scan signal S1 is applied to the first gate line 111, the EL elements constituting the R, G and B unit pixels (PR11-PR1n), (PG11-PG1n), (PB11-PB1n) of the pixels P11-P1n connected to the first gate line 111 are driven at the same time.
Likewise, when the scan signal S2 for driving a second gate line 112 is applied, data signals D(S2) (DR1-DRn), (DG1-DGn), (DB1-DBn) from the R, G and B data lines (121R-12nR), (121G-12nG), (121B-12nB) constituting the first to the nth data lines 121 to 12n are applied to the R, G and B unit pixels (PR21-PR2n), (PG21-PG2n), (PB21-PB2n) of the pixels (P21-P2n) connected to the second gate line 112.
The EL elements constituting the R, G and B unit pixels (PR21-PR2n), (PG21-PG2n), (PB21-PB2n) of the pixels (P21-P2n) connected to the second gate line 112 are simultaneously driven by the driving currents corresponding to the data signals D (S2)(DR1-DRn), (DG1-DGn), (DB1-DBn).
By repeating such operations, when the scan signal Sm is finally applied to the mth gate line 11m, the EL elements constituting the R, G and B unit pixels (PRm1-PRmn), (PGm1-PGmn), (PBm1-PBmn) of the pixels (Pm1-Pmn) connected to the mth gate line 11m are simultaneously driven according to the R, G and B data signals D(Sm) (DR1-DRn), (DG1-DGn), (DB1-DBn) applied to the R, G and B data lines (121R-12nR), (121G-12nG), (121B-12nB).
Therefore, if the scan signals S1-Sm are sequentially applied from the first gate line 111 to the mth gate line 11m, the pixels (P11-P1n)-(Pm1-Pmn) connected to each gate line 111-11m are sequentially driven, thereby displaying a picture by driving the pixels during one frame 1F.
However, in the OLED having the above structure, each pixel is composed of three R, G and B unit pixels, and by each R, G and B unit pixel, the driving devices, that is, a switching thin film transistor and a driving thin film transistor and a capacitor, for driving the R, G and B EL elements, are arranged. Further, the data line and a power supply line for providing the data signal and the power supply (ELVDD) to each driving device are respectively arranged in each unit pixel.
Therefore, for each pixel, three data lines and three power supply lines are arranged, and at least six transistors, that is, three switching thin film transistors and three driving thin film transistors, and three capacitors are required. Further, for each pixel controlled by a light emitting control signal, a separate light emitting control line for providing the light emitting control signal is required. Hence, the conventional display device has problems in that, as a plurality of lines and a plurality of devices are arranged in each pixel, a circuit constitution is complex, and thus, a probability that a defect is generated is increased, thereby lowering yield.
Further, there is another problem that as the display device becomes high definition, each pixel area is reduced, and thus, it is difficult to arrange many devices in one pixel, and the aperture ratio is also reduced.